The present invention related generally to lifting devices, such as cranes or the like, and more particularly to a complementary locking and latching system for a telescoping boom.
Various types of telescoping booms or boom assemblies for use in cranes or other lifting devices are known in the art. The conventional boom assembly includes a plurality of nested tubular sections, with each outer section having larger cross-sectional size than the next-adjacent inner section to permit the desired relative telescoping movement. In the typical arrangement, the proximal end of the outermost boom section is pivotally mounted on a turntable and the distal end of the innermost section carries one or more sheaves or equivalent structures for supporting the hoisting cable or the like.
Usually, to telescopingly move (extend or retract) a selected boom section relative to a next-adjacent boom section, a motive device such as a boom xe2x80x9cextensionxe2x80x9d cylinder is employed. This extension cylinder is often positioned inside the innermost boom section, with the proximal end of the piston rod (often called the xe2x80x9crod endxe2x80x9d of the cylinder) either pivotably or fixedly mounted to a stable structure, such as the endwall of the outermost boom section or an adjacent component of the crane. To couple the selected boom section to the xe2x80x9ccasexe2x80x9d end of the extension cylinder, a latching device may be provided. Such devices often include opposed pairs of transversely movable structures that, in a latched position, project through corresponding apertures formed in the sidewalls of the boom section selected for telescoping movement. Hence, when the latching device is in the latched position and the extension cylinder is extended or retracted, the selected boom section telescopingly moves toward the corresponding extended or retracted position relative to the next-adjacent boom section.
Either after the latching operation is completed, or at substantially the same time, a locking device, such as a spring-loaded pin that is normally biased to securely hold the selected boom section in place, is retracted. Then, once the selected boom section reaches the desired position as the result of the relative telescoping movement, the operation is reversed such that the locking device is moved to the locked position and the latching device is retracted, in that order. Consequently, the boom section previously selected for telescoping movement is locked in the extended or retracted position. The latching device may then be used in combination with the extension cylinder to telescopingly move another selected boom section (with the locking device associated with that selected boom section being retracted and released as described above).
While this dual locking and latching arrangement works well for its intended purpose, efficiently and effectively moving the latching device between an unlatched and a latched position, retracting the locking device, and then reversing these operations when the selected boom section reaches the desired position is somewhat difficult in practice, especially within the confines of the boom assembly. Others in the past have proposed different types of motive devices for separately actuating the latching and locking devices, but most are exceedingly complex in design and in some instances may even be unreliable in operation (thus necessitating separate xe2x80x9cfail-safexe2x80x9d devices, which may include auxiliary motive devices, including hydraulic cylinders, or even manually operated locks).
For example, some less than advantageous features required in a few past arrangements include the need for actuating the locking and latching devices using multiple, completely separate motive devices, such as hydraulic piston/cylinder combinations positioned orthogonally to each other (see, e.g., U.S. Pat. No. 5,628,416 to Frommelt et al.), or using multiple motive devices in combination with corresponding complicated hydraulic control systems (see, e.g., U.S. Pat. Nos. 4,433,515 and 4,490,951, both to Mentzer et al.). In addition to a separate latching device, a more recently proposed system requires two spring-loaded locking pins positioned in the opposing sidewalls of each telescoping boom section, with each pin being actuated by a separate hydraulic cylinder (see, e.g., U.S. Pat. No. 6,216,895 to Erdmann et al.). While these systems may be effective, the requirement of using more than one motive device to effect the locking and latching operations contributes to their complexity. A direct correlation exists between complexity of the locking or latching system and not only the expense to construct, operate, and service the boom assembly, but also the overall weight and minimum size requirements.
Accordingly, a need is identified for an improved, yet simplified, complementary locking and latching system for use. with a telescoping boom assembly. In one aspect, the locking and latching system would include locking and latching devices that are essentially independent of each other in form, but work together or complement each other in operation using a single motive device. As compared to past proposals, the resulting system would thus be somewhat less complicated in design, less expensive to manufacture and install, and easier to service. In another aspect, the invention would not necessarily be limited to the use of a single motive device, since a more efficient manner of automatically retracting or releasing a locking device immediately after moving a latching device between the latched and unlatched positions would be provided. In an even more specific aspect, the locking and latching system would be relatively compact, and thus would easily fit within the confines of a conventional boom assembly. In certain applications, the compact nature of the system would even allow for use with telescoping boom assemblies having smaller dimensions than previously thought possible, without compromising the strength and lifting capability, necessitating extensive redesign, or requiring special miniature components. In yet another aspect, the system would be designed so as to minimize the weight contribution to the overall boom assembly. In final analysis, the system in all respects would be an improvement over those in the prior art in terms of efficiency and reliability, which in turn would reduce operational costs.
In accordance with a first aspect of the invention, a system for selectively latching and unlocking a selected boom section for telescoping movement relative to a next-adjacent boom section is provided. The system is especially adapted for use in a crane or lifting device having a telescoping boom assembly including at least two boom sections and an extension device for telescopically moving the selected boom section relative to the next-adjacent boom section. The system comprises a latching device for latching the selected boom section to the extension device in a latched position, a locking device for locking the selected boom section in place relative to the next-adjacent boom section, and a single motive device. The motive device includes a locking and latching cylinder for moving the latching device to the latched position and moving the locking device to an unlocked position prior to telescopingly moving the selected boom section, and then moving the locking device to a locked position and moving the latching structure to an unlatched position when the telescoping movement is completed.
In one embodiment, the locking and latching cylinder is supported by and axially aligned with the extension device. The locking and latching cylinder is also coupled .to an engagement head forming part of the motive device for moving the latching device between a latched position and an unlatched position. The latching device may include at least two pivoting latching plates (and preferably two pairs of latching plates, with one pair positioned on each side of the extension cylinder). Each plate includes a hook-like portion for projecting through a corresponding aperture in the selected boom section and a specially contoured camming surface. The engagement head of the motive device may include a pair of opposed. projections for simultaneously engaging the camming surfaces to move the latching plates into the latched position during extension of the locking and latching cylinder and to an unlatched position during retraction of this cylinder. As a result, efficient and effective latching action is reliably achieved.
The motive device may include a pivoting bellcrank for retracting a locking pin of the locking device when the latching plates are positioned in the apertures in the selected boom section. Furthermore, the engagement head of the motive device may include a bearing structure for preventing the bellcrank from pivoting when the locking and latching cylinder is in an extended or home position. In one embodiment, the movement of the engagement head moves the bearing structure away from the bellcrank, which may then pivot to retract the locking pin and allow for the extension or retraction of the selected boom section using the extension device. Alternatively, at least one, and preferably both of the latching plates may carry a bearing structure for preventing the bellcrank from pivoting. The movement of the latching plates to the latched position thus moves the support away from the bellcrank, which may then pivot to retract the locking pin and allow for the extension or retraction of the selected boom section. The bellcrank may be U-shaped, and the locking pin is coupled to a receiver, which may have an I-shaped cross-section. The receiver thus includes opposed channels for receiving opposed cams projecting inwardly from the sidewalls of the U-shaped bellcrank. The engagement between the cams and the corresponding surfaces of the opposed channels formed in the I-shaped receiver thus serves to retract and release the locking pin as a result of the pivoting of the bellcrank.
In addition to a locking pin, the locking device may further include a compression spring for normally biasing the locking pin into a corresponding opening in the next-adjacent boom section when the selected boom section is a certain position, such as the home or extended position. The pivoting action of the bellcrank serves to overcome the biasing force of the compression spring to disengage the locking pin from the corresponding opening. The selected boom section may then be moved as desired as a result of the coupling formed with the latching plates associated with the extension device.
Preferably, the piston rod of the locking and latching cylinder is coupled to the pivoting bellcrank. Consequently, during retraction of the locking and latching cylinder, the movement of the piston rod assists in pivoting the bellcrank to move the locking pin. Specifically, when the bellcrank is pivoted from a home position, the locking pin of the locking device is fully retracted from the opening in the next-adjacent boom section, thereby permitting telescoping movement of the selected boom section. When the bellcrank is returned to the home position, the locking pin is moved to the locked position to prevent the relative telescoping movement.
In a more specific embodiment, the locking and latching cylinder is coupled to a movable support frame supported by the extension device. This support frame includes first and second projections, each having an engagement head, and the latching device includes first and second pairs of spaced latching plates. The pairs of latching plates are simultaneously moved toward a latched position by the engagement heads of the projections when the locking and latching cylinder is retracted and moved toward an unlatched position when this cylinder is extended. The first and second pairs of spaced latching plates may be positioned above and below the extension device, or in any other orientation desired.
In accordance with a second aspect of the invention, a telescoping boom assembly including at least two boom sections and an extension cylinder for telescopically moving a selected boom section relative to at least one next-adjacent boom section is provided. The boom assembly comprises a latching device associated with the extension cylinder. The latching device includes at least one latching structure for engaging the selected boom section in a latched position. A locking device is also associated with the selected boom section, with the locking device including a locking pin for locking the selected boom section in place relative to the next-adjacent boom section. The boom assembly further includes a locking and latching cylinder having a first longitudinal axis axially aligned with a second longitudinal axis of the extension cylinder. The locking and latching cylinder is capable of moving the latching structure into the latched position. and moving the locking pin to an unlocked position such that the extension cylinder may be used to telescopingly move the selected boom section between positions, and then moving the locking pin to a locked position and moving the latching structure to an unlatched position when the telescoping movement is completed.
In one embodiment, the locking and latching cylinder is supported by a movable support frame, which is in turn supported by and moves with the extension cylinder during extension and retraction. In particular, the support frame may slide along the extension cylinder as the locking and latching cylinder is extended and retracted to activate the locking and latching devices. Preferably, at least one wear pad is positioned between the support frame and an outer surface of a case of the extension cylinder to create desirable low friction contact.
The telescoping boom assembly preferably includes a plurality of boom sections, as noted above, such as at least two inner boom sections that are capable of telescoping movement relative to an outer boom section. Each of the at least two inner boom sections includes a locking pin. The locking pins form part of the locking device.
In accordance with a third aspect of the invention, a system for selectively latching and unlocking a selected boom section for telescoping movement relative to a next-adjacent boom section is provided. The system is especially adapted for use in a crane or lifting device having a telescoping boom assembly including at least two boom sections and an extension cylinder for telescopically moving the selected boom section relative to the next-adjacent boom section. The system comprises at least one pair of latching plates associated with the extension cylinder for engaging the selected boom section in a latched position, at least one locking pin for locking the selected boom section in place relative to the next-adjacent boom section, and a motive device including a locking and latching cylinder. The locking and latching cylinder is coupled to a support frame. The support frame includes at least one engagement structure for engaging and moving each of the latching structures to a latched position and a pivoting retraction structure for moving the locking pin from a locked position when the locking and latching cylinder is actuated.
In one embodiment, the engagement structure includes at least one projection extending from the support frame in an axial direction. The projection includes an engagement head having opposed structures, each for engaging and moving one of the pair of latching plates to the latched position. The pivoting retraction structure includes a bellcrank that pivots to move the locking pin to an unlocked position. One of the projection or the pair of latching plates carries a bearing structure for preventing the bellcrank from pivoting until the latching plates are in the latched position.
In accordance with a fourth aspect of the invention, a method of telescopingly moving a selected boom section relative to a next-adjacent boom section in a telescoping boom assembly having an extension cylinder is provided. The method comprises actuating a latching device to latch the extension cylinder to the selected boom section using a motive device including a locking and latching cylinder, actuating a locking device to unlock the selected boom section from the next-adjacent boom section using the locking and latching cylinder, and then telescopingly moving the selected boom section using the extension cylinder. The method may further comprise the steps of: (1) releasing the locking device to lock the selected boom section in place; and (2) moving the latching device from engagement with the selected boom section. Preferably, the locking device is moved to the locked position before the latching plates are moved into the unlatched position.